Ixodes scapularis transmits important pathogens to humans, including the causative agent of Lyme disease, Borrelia burgdorferi. Lyme disease is the most commonly reported tick-borne disease in the United States. Tick salivary gland molecules are essential for modulating host innate and adaptive immune defenses and for transmission of infectious agents. Ixodes scapularis infestation polarizes host T lymphocyte cytokines to a Th2 profile while suppressing Th1 cytokines. Passively reconstituting suppressed cytokines provides protection against tick transmission of B. burgdorferi. This proposal is based on the hypothesis that reversal of I. scapularis induced Th2 polarization of host CD4+ T-cell responses will provide protection against tick transmission of B. burgdorferi. A well defined in vivo T-cell receptor (TCR) transgenic adoptive transfer model will be used to study the influence of infestation with pathogen-free and infected ticks as well as isolated tick salivary gland molecules on responses of naive CD4 T-cells to specific antigen. The first aim is to characterize the influence of infestation with pathogen-free and B. burgdorferi infected I. scapularis on the cytokine producing ability of TCR transgenic clonotypic T-cells specific for a model antigen, influenza hemagglutinin, on B10.D2 and BALB/c genetic backgrounds, which differ in their support of Th1 and Th2 responses. Second specific aim is to identify, isolate and characterize I. scapularis salivary gland molecules responsible for polarizing transgenic CD4 T-cells to a Th2 profile. Genes encoding reactive molecules will be cloned, recombinant forms expressed in a eukaryotic expression system and tested for activity. The third aim is to immunize with the recombinant forms of the reactive salivary gland molecules and determine whether tick induced cytokine polarization and B. burgdorferi transmission are blocked.